I'm looking for a 40mm ish diameter countersink bit. I want to make a small 'lead in' on my throttle bodies which are 35mm dia. Ideally I just need to borrow one for a day or two but if one is available for a reasonable price I might be able to find some beer tokens

Valve seat cutter???

Now why didn't I think of that?

Or any cutting tool (router bit?) designed for wood will work fine - assumiming the parts are ally.

Cheers

Fred W B

Good call Fred

Or even a deburring tool, these work nicely on aluminium. If you just want to take a little off.

http://www.cbsonline.co.uk/swivelling-blade-deburring-tool-swdeb-838-p.asp

Cheers Matt, I think the router bit like this one

would be the best option as it gives a rounded profile which is perfect for gas flow. I just need to find one at B&Q (that one is only £7 but from Hong Kong) or similar - only need a cheap one as it will only get used once or twice.

*edit* Just found one on eBay for £7 and free p&p

[Edited on 8-12-10 by RazMan]

Just make sure you turn it carefully/slowly, maybe by hand?

Fred W B

[Edited on 9/12/10 by Fred W B]

The thought of applying that router bit to the end of an aluminium tube terrifies me...

...they're scary enough when used on the edge of a big slab of wood!

Yes, and in the cold light of day I have had slight re-think (I had dreams about flying swarf last night )

I think a golf ball with a bolt through the middle might act as a shaped holder for some emery cloth. Using a cordless drill and pushing the ball/emery into the opening of the TB, it shouldn't take too much effort to give me a small lead-in.

but it has given me an idea ..........

What is the opposite shape to the "rounding over" shape?

Ie the rounding over bits 'cut' is the inside of a circle, i want the cut to be the 'outside' of the circle?